Hope this helps.........
If you have a chance to get an RT cheap, pick it up. The lvl 10 will fit on it and it will work great. Same great customer service as all AGD markers. I just bought another one for $200 bux. Not a bad investment. You SHOULD be able to find one under $350. I would buy one quick though after AGD starts realy advertizing the lvl 10 they will be very hard to get and not as cheap.
About the valves.
I'm a certified RT tech. From what I can remember the difference in the valve (besides dimentions) is that in the Classic RT the top of the valve pin is slightly bigger. Because of this you can get a slightly more reactive trigger (more push with less pressure) than on the Retro-valve. Now this increase will be small but it is possible. They will cycle at the same speed!
The original RT stood for REACTIVE TRIGGER the new RT stands for RETRO VALVE.
Hope this info helps you out some.
AGD Classic RT
WGP Cert. Tech
AGD Cert. Tech