To be honest I really don't share Dwayne's concerns about IV use of RCs. Street drugs are way dodgier and nobody sees shooting them as such a big deal if that's what somebody wishes to do with them. It would have to be some pretty nasty contamination for it to be a big concern IVing something - anthrax wouldn't be wise - but you'd still be at risk using anything that contaminated orally. Fuck, some of the horribly impure street drugs cut to hell with fuck knows what that I've shot up boggle the mind but have never once boggled the body. That's not to say IVing anything is necessarily wise... but it really isn't half as risky as some seem to think.
OP: I would definitely recommend not shooting any 2Cs cos they all seem to fuck with the body - especially the heart - to varying levels of discomfort. Doesn't feel very safe and, to be honest, it's a shitty ROA for them even if it felt totally safe.
IV 4-AcO-DMT was amazing but unbelievably intense. I'd suggest 5mg as a pretty strong dose with 10mg being a complete disconnection with reality for a while. You have no clue what's going on and can barely see for all the visual distortion. Have never gone higher and really don't feel the need to cos I doubt you'd remember much of anything if you did. It felt "safe" compared to shooting 2Cs but the intensity is overwhelming - very similar to IV DMT according to folks who've shot both. Don't underestimate the potency of the stuff if you do try to shoot it - 5mg may look like a stupidly small dose that would do sod all but believe me it does. It is nothing like oral dosing - not exactly recreational and no use for social tripping. It's very much a short, sharp shock. Can also be rather fiendish due to the brevity of the experience - a strong contender for the "Hippy Crack" crown, for sure.
Check out the 4-AcO-DMT IV subthread - think it's linkied in the first post in the main 4-AcO-DMT thread or search for it. Myself and others described it in more detail there - worth a read through but some of the doses suggested are just plain silly and irresponsible, in my opinion.