The Syrus version of T400 is painless for most users. 300mg of 400mg is composed of testosterone esters (enanthate and decanoate) that cannot possibly crystallize at the injection site.
Denkall T400 hurts, mainly because it it has a high content of Cyp, which is not nearly as oil soluble as Decanoate or Enanthate. It also has a little bit of Prop which I'm sure doesn't help with the pain factor.
Denkall T400:
Testosterone Propionate 25mg
Testosterone Enanthate 186mg
Testosterone Cypionate 186mg
Syrus T400
Testosterone Enanthate 100mg
Testosterone Cypionate 100mg
Testosterone Decanoate 200mg