You might see some difference in performance, a bmp is most times uncompressed data, so can be read & displayed quite quickly, while a jpg must be decoded to an image first, but then i would hazzard you would only notice it on huge images, and even then it might be compensated for becuase the jpg might save time on the disk reads as its significatly smaller in size than a bmp.
All up, i doubt you could spot the difference. (unless there is some other element to ther draw speed im not aware of)
))