The basic was actually pretty fast for what it was; certainly compared with the Spectrum's basic which gobbled up memory and speed on number storage. For any decent speed, though, assembler was the way to go. Technically, it had a 6510 rather than a 6502 because of the IO ports on locations 0 and 1.
A tedious processor to use, though, having to shuffle everything through the Acc and zero-page.