Storing user patches on the Ti...
 

...is there empty slots, or do you have to overvrite existing sounds?

Quote from access> Extended memory: 512 RAM patches and 2048 ROM patches (rewritable)

I think everything in the RAM bank when you get it are also in the ROM - there was a post about this somewhere giving more details.

So over-write whats in the RAM.

I'm wondering this at the moment, I'm sure there's a preferable one (ROM or RAM?) to save user patches in but can't remember which.

I would say ram is preferable to rom for overwriting sounds (as a general rule) rom = Read Only Memory is typically where the original sounds reside and ram is where a copy is stored to be tweaked and overwritten. In the older days, rom slots couldn't be overwritten, so you only had ram slots to work with though, if I read the manual correctly, on the TI both ram and rom slots can be overwritten. Plus I think you also have a set of favorites slots to use as well.

RAM A = ROM B
RAM C = ROM D
RAM D = ROM E

RAM A = various patches all over ROM banks

I just overwrote RAM A-D with the INIT patch, so now I know what is what.