I've never thrown Crushes, but, like any mold, each disc can vary in stability, based on how domey it is, the plastic type, and the weight. Flat to moderate domed forces aren't really overstable at all, especially at high speeds, while domey Forces are suuuper overstable.
I will flick moderate domed Forces flat on holes 300-420ish, because I know the disc very well, and it is super predictable for me, wind or no wind. If 300-350 is your current range, I wouldn't recommend a Force as your main driver. You aren't getting the speed or rpm's up enough to utilize that disc. Any number of slower discs will likely get you more predictability (and less skip) in that range. Probably Orc's, Crushes, Z Flashes, Firebird FL's, Surges, etc..
For a standstill drive, your distance range sounds very good. You will also be more accurate, and consistent with less runup. To throw further than 350', you will likely need to introduce more runup. A couple steps should suffice to generate a lot more power from the legs/hips/torso and then finish with shoulder/forearm/wrist.
450-500+ foot forehands are world class, that's for sure. I'm 6'1'', 200lbs, come from a racquetball background, and perform precise resistance training and flexibility exercises weekly to maintain/improve the muscle power and range of motion to throw sidearms that far. When I was new to disc golf 3 years ago, I would throw the huge anhyzer line you described, with a Z Flick. It was just brute power, very ugly I'm sure, and definitely painful to throw more than a few times per round. I would not even play on back to back days because my shoulder would be that sore the next day. My max D with that style was 480' on flat ground. The height used had to have been 30' +, and the angle used was so severe that a lot of my shots would turn into sky rollers. My elbow was very far away from my body, and my shoulder was generating most of the power (both can be dangerous, and not worthwhile).
This year, I cleaned my form up quite a bit, and I throw most of my sidearms flat. My shoulder doesn't get nearly as sore, and I can play back to back days. For golf lines 450'+, and even in distance competitions, I throw very low to moderately high (10'-20') line drives most of the time. If it is a tunnel shot, or I don't want any turn left, I will throw a moderate domed ESP Force, or a similarly shaped 1st run champ. boss. that is newish. If I can afford, or want some turn left, for a huge "S" shot, a 169ish star boss, or more beat 1st run champ. boss will do that for me. If I want a very long (450+) right to left the whole way, I will throw my flat or moderate domed worn in 1st run and/or star destroyers, flat and or worn esp forces, or if there is a headwind, the 1st run champion boss with a little bit of anny.
For pure distance, in competitions, I will sometimes throw anny with overstable discs, and they usually go 450ish on flat ground. The shots that actually went the furthest (495'-516') surprised me. They went right to left the entire time, and never came back to the right at the end. For me, the perfect discs for that max D were 171-172g esp forces or star destroyers that were flat to very slight dome.
I tried the Pulse once, didn't like it much, and definitely wouldn't recommend it for reaching new levels of sidearm distance.
Maybe Discraft has sold a few more of them with Geoff B.'s quote, though. I believe the official sidearm distance record is still Scott Stokely's 518.3' ?? I wouldn't be surprised if a handful of people have unofficially thrown further on flat ground (Geoff included), but 610' on flat ground hasn't happened. Maybe the equivalent of a 95+ mph sidearm pitch, at the right height could go that far...maybe. I am actually trying to figure out how to get that last 24' or so to break the record, if it still stands as the record. Maybe a hyzer flip will do it (something I've yet to try), with a flippy destroyer/force/wraith/something else?
At the Vibram Open at Maple Hill this year, I was probably the only one throwing sidearms in the distance comp. and threw 514' with a 175 1st run champ. boss, and 516' with a 172g esp force (12th best maybe?, top 10 made finals I think). I don't think Geoff B. even threw, because the top guys throwing backhand are in a different league, and were certain to take the cash. The tee is elevated maybe 20'-25', but I threw all line drive annys that didn't really take advantage of it. The reason I say this is because I threw 495' (laser fancy gadget measured) a few weeks earlier on flat ground. I thought the 2 good throws I had were easily the longest I had ever thrown, and expected them to be 550'-600' because of the elevated tee, but was surprised that they were barely further than the flat ground throws I had in the 495' range a few weeks earlier.
It's not a great time of year in New England (snow on the ground, freezing temps) to try these throws now, but Tim Red Beard might take some video of my sidearm throws this weekend, if we have time for a fun distance competition. My style is very compact, and much different from Geoff B. and Ville's styles. Geoff B. uses a huge range of motion, starts with the disc vertical, reaching way back and following through a ton. Ville Piippo looks to have great range of motion in his shoulder, but doesn't use a lot of lower body at all in the videos I have seen. I use a lot of lower body, core, and forearm but don't follow through very much (this will hopefully change and increase my power and decrease stress on the body).
The Mark Ellis Discraft video on youtube shows some great form (especially Mark's), that could help you in the meantime.
Oh, wait, the moral of the story is: develop those callouses if you want to sidearm 450'+...and go to the buy/sell/trade section and check out my discs