mrA, I am assuming that you have an A500. So basically what you are saying is that I should get 3.0 Roms and run WB3.1? (or 3.1 Roms w/WB3.1) Is this the optimal set up for an A500 (btw I dont even have the ECS yet.. my system is circa late 80s)
Yes, I'm using my A500 to type this. If you're buying a ROM, it's best to get 3.1 or if you've already got a 3.0 ROM there's no need to get 3.1. Either way, you can run WB 3.1. If you really want to run WB3.9, go ahead. I just found it worse than 3.1 in my own experience.
The main reason for ECS Agnus is for more Chip RAM. I think you can still run WB 3.1 on the original Agnus, but you will run out of display RAM much faster. You can easily run without the ECS Denise. ECS Denise only gives a couple super-high-res display modes (totally useless) and the ability to have the screen border black (which is nice). I ran WB3.1 with original Denise for a year - no problem. (but I'm still glad I got it for the nifty borders)
I think the Viper really is the best accelerator because it has the A1200 3.0 ROMs on the card. This alone makes my A500 run about twice as fast as having the 3.0 or 3.1 A500 ROM in the original ROM slot (can see it in speed tests). So if you get an accelerator that doesn't have ROMs on it, the ROM reading will be the bottleneck unless the card allows you to map it to Fast RAM (I think the Derringer does).