If you use a script, you want it to ONLY remove the bytes on a failed receive... not when you get a resume. That reduces the chance of problems. Of course, with a 1MB truncation, it is very easy to lose the entire file no matter what.
If people use 4096 (the best packet size for 99% of users), then the 8k truncation works just fine. Yes, 8k packets can be faster on some connections, but only if the sender and receiver can get 8k packets without packet loss. In most cases, the 4k packets are faster from what I've seen with the different sizes.
The only way to tell for sure is to test overall speeds (send a 10MB file to 10 people using 4k packets and check total time.... then repeat to the same 10 people using 8k packets). You need a decent file size for it to be accurate because speeds increase and decrease often and you need to see overall speeds.
