The half life is different by only about a day. Where you could have an issue would be if that you were on only a marginal injection frequency already, such as once per week or even less frequent, then it would be even more marginal if using testosterone enanthate. However, if injecting at least 2x/week already, then there would be no need for adjustment.
Use the 250 mg figure. It's a potentially confusing aspect of pharmacy: some drugs are referenced by the weight of the active part of the molecule (for example, Nolvadex is labeled and prescribed according to the weight of contained tamoxifen, though the product is tamoxifen citrate ) and others are referenced by total weight of the molecule (for example Clomid is labeled and prescribed according to the weight of clomiphene citrate: the actual amount of clomiphene delivered is less than the prescribed and labeled amount.)
Testosterone esters fall into the second category. All references are to the total weight.
While in theory it would make sense to figure amount used according to the amount of contained testosterone, in practice that's a fine tuning that almost always is not done, a partial exception being testosterone propionate due to, in that case, a more substantial difference in percentage testosterone contained.
Or a briefer answer compared to that relatively lengthy one: the difference resulting from different weight of ester doesn't need to be accounted for and almost always is not accounted for, as dosing is rarely extremely precise anyway. For example, no one injects 71 mg at a time. Perhaps 50, perhaps 75, perhaps 100: almost always rounded numbers. Ester weight difference would be aiming for more precision than is lost in the rounding process.