The RCA card shouldn't make any difference.Interesting, also reading my previous post I forgot to mention that RCA input card disables all video output from the machine I had to remove it to get an image lol. But I wonder what this could be clocked too?
WRT Over clocking your machine, 6x looks like the max, so you'd desolder the 40MHz crystal Oscillator and replace it with a socket, then get a collection of crystals between 40 and 50MHz and test to see how fast it remains stable, then back off a few %. This would be raising the bus speed, rather than the multiplier.
Personally, you have the fastest 6360 out there with a stock board, and its special. I wouldn't change it.
If I did want a faster 6360, I'd just put a 6500 board in it rather than messing about soldering.