Most likely not at all on a XL as there are hardware restictions that can be solved with my versions based on DSA.
As for the X10 models it is a matter of testing, some V9 NC's give you more other won't work at all.
If you use a NC with a SE ttsystem adjusting the switchfiles is a must as you won't get results otherwise.
And again : The best NC is always what Home offers as an official update - all other NC might work fine but there can't be a guarantee.
The NV with the highest version number is not always the best either.
All V9 NC's offer similar features, main difference to the V8 is the 3pane status bar - not more...
Only the 9.4xx NC offer new options for the speedcams which is not really that important anyway.
So if you have a older device and you are after reliable navigation and not the latest gimmiks it might be good to use a trusted V8 like the 8.412, 8.562 or the 8.398 instead of a V9.
Especially 32mb models will benefit from the memory savings and can often use computervoices as well.