5-speed fifth is useful at 40mph or higher (on a 1200 at least). It will give you better highway fuel economy and lower engine wear both. The B210s got 47 mpg with this trans, while 1200s with a smaller engine only got 38 mpg. Easier on the ears too.

However, the 63a is heavier, so it'll make your car a bit slower accelerating. So probably not the best for drag racing. You probably couldn't tell the difference on the street. But in-town fuel economy will suffer a bit. The 60- 5-speeds are also heavier, but not as much as the 63- series

The gearing will be very different from the 1200's gearbox. You may find you like the spread better, even for low-speed driving (or you may find it worse). The gear ratios are listed in the Tech Section 5-speed overview article.