Can't speak of SP but I know if I've ever had anything I wanted looking at on a Angel, it's always been back to me sorted within two business days of WDP receiving it.
However back on topic...
A4 or Speed. The answer is whichever you can afford. Zero actual tangible performance difference between the two markers.
Weight difference if neglible
A4 has safe to live mode which some hate and some love (I like it as I don't have to recalibrate Sensi each time I power on)
Locking feedneck on A4 which saves having to sand a hopper feedneck down
A4 comes with the volumisers as standard
LCD is a bonus if you like that sort of thing
If you have already got a Speed I would stick with it and use the money saved to buy lots of paint so you don't have to hold back the next few times you go out and let rip with it