I upgraded my XT with a NEC V20 and got the boot time down to 60 seconds! Of course, I also had a 10 MB HD, a trade-off for keeping the green screen. </four yorkshiremen>
A hard drive would have been a definite improvement over all the disk swapping I did, maybe worth trading for a bw monitor. Actually mine was 4 colors including black and white. The other two were red and cyan. I feel a little guilty over selling that computer, however. It has a “turbo” function which I forgot to tell the buyer about (Ctl-alt-+). He probably never found out.
The PC Transporter coprocessor card for the Apple II I have around here somewhere, uh, I think it is, anyway, that used an NEC Vsomething processor.