Personally I think I'd go with the
L5460 for a primary/only tractor given how little difference there is in advertised performance/specs there seem to be between the two.
On the other hand I'd probably get the MX5400 if it was going to be used as a secondary tractor given it's cheaper (or the geared transmission & factory 7 pin trailer connection were needed).
Just for consideration depending on what is being done that extra 200lbs of weight may come in handy (plus whatever wheel weight/liquid
ballast can be added); as currently configured my
L3560 may actually weigh as much as an MX5400 and (unless I'm doing something boneheaded) it's usually traction limited rather than power limited (especially when working in low range) when pulling or digging.
This might just be me, but I've found many of the "luxury" features on the Grand L series helpful in being more productive. For example: the HST+ transmission has been really handy to change speed/power capabilities on the fly without having to change the overall range. Likewise the stall-guard has been handy a few times while mowing in a pasture and I've ended up in grass that was thicker/wetter than I expected.
Of course, that being just my opinion on the value of the "luxury" features it might also be worth checking resale potential of each in your area (especially if there's a possibility of needing to sell it later) as that seems to vary by region/product level.