Anything over 300 is fast no matter where you are in the game, but I remember a long period of time when my best toons were in the 250-270 range, and I had struggled through months before that when 230 was considered blazing. Ah, the innocent days before mods!
These days it's important to recognize that different toons have different base speeds. So while 450 might be an objectively fast speed, if you're comparing one GL Rey to another, 450 is going to be considered slow.
So a better measure is to compare mods. Does a particular set give you +80? That's not a fast set, since you can get that with a speed arrow (+30) and 5 mods with +10 each on the secondaries. If you're rocking a +80 set, it better be doing more for you than just speed. In fact, if you're using a set of 4 speed mods and the combined speed advantage from your speed arrow primary, your speed secondaries, and your speed set bonus (of +10%, so it changes depending on the toon you put it on) is a total of +80, then that's actually going to be considered bad. (Although if you're an early player just starting to collect mods it still might be the best you have for your first month or two.)
I have a set of 4 CritDamage mods and 2 Crit Chance mods that includes an Offense primary ability on the arrow instead of speed. It includes a critical damage triangle and an offense primary on the plus. The total speed bonus is only +100, but because the set is primarily built to do as much extra damage as possible, +100 as a mere secondary function is quite good!
So first you have to look at the question, Is the primary purpose of this set to get faster? If so, you'll want at least +120 from the primary and secondaries, and then the +10% set bonus for having four of your mods be speed set mods. This will net you about +133-138 these days and would be considered (at least by me) the low-end for a good set of speed mods.
If the primary purpose of the set to do something else? Well, then if you have a speed primary on your arrow, then +115 or +120 would probably be the bottom end of a "good" set of mods that are designed to do something else, but still have a significant emphasis on speed.
If the primary purpose of the set is to do something else and you sacrificed +30 speed on your arrow to get a different primary ability that furthers the core role of that set of mods? Then I'd consider the low-end of "good" to be about +90.
Anyway, that's merely my opinion, but you did ask.
