I have read the tutorial and searched the forum...

I was wondering if there was a point when the card speed would affect the device performance?

Obviously the faster the card... The faster the nc will load...

Apart from loading the nc would the card speed affect normal operation like route planning?

I guess card speed would be more important on 32MB devices...?

Can anyone tell if I was to use a class 4 card if I would experience lag during normal operation ?

The speed is no longer that important these days as even normal SD cards are fast enough for the normal needs.
I use an old 128mb SD card for testing and it takes ages (compared to my 16GB SD) to copy data on it, but during normal GPS use I see no difference in performance at all.

Thanks downunder

Great example.... I was concerned that the class 4 device I ordered would not be adequate speed wise... Now o am sure it will be fine :-)

Class 4 should be enough to watch movies with Tomplayer (you have to re-encode the video though).

I find the faster speed of the newer cards only makes a difference when reading/writing large files to the card, Which doesn't happen on PNA'S Executing files is down to the processor speed of the host device, Some of my devices have first generation SD cards installed and there's no difference in speed.

The bottleneck isn't the processor, but the read/write speed of the cardreader. Slow cardreaders are more than fast enough for GPS purposes. But I haven't tested it at 250 KM/h ;)

Oh yes, correction. I did! Even faster!! While flying to my holiday destination!
So, no problem to expect when normal use.