I think I have read somewere, that trapdoor ram, used as chipram is not the fastest solution. Will there be differences in speed between upgraded chipram on the board versus chipram in the trapdoor?
I think you misunderstand the difference between chip ram and fast ram. True, chip ram is not as fast as fast ram (which, on an A500 typically sits under the CPU or in the expansion slot on the side), however it is directly addressable by the custom chips - which means you can (generally) load larger mods, open screens with higher resolutions and more colors, play games with more graphic objects, etc. A loose analogy is to think of it sort of like the difference between motherboard ram on a modern PC and graphics card ram.
Note that this is different from cards like the AdRAM, which add additional memory physically inside the trap door slot and call it "fast ram" but which don't actually provide the speed boost of real fast ram.
TL;DR. It's best if you can max out both your chip and your fast ram, budget permitting, of course.
