If you are using a 5x7 or 8x10 enlarger, I would recommend to buy a 150mm lens for 4x5. 135mm is usually a better choice for a 4x5 enlarger. Reasons:
- 135mm hardly covers 4x5 - you have to be much more precise in positioning a 4x5 in a 5x7 carrier. The coverage of a 150mm will save you some nerves.
- a 135mm will provide lager mag-ratios on a 4x5 enlarger