The reason translating version is faster because in each iteration it doesn't have to do any trig, just simple addition. Trig only involve in battlefield rotation (at the beginning and at the end). This is the reason this version is faster.
Glacier does the interpolation while recording scans, instead of during PIF, but same effect really.
Edit: Err... I got mixed up by the page title being "interpolating PIF" which I'd strongly expect to refer to interpolating missed scans. But yes, Glacier does use translating PIF.