OPS isn't "in" an aircraft. It's a performance calculation system developed by Texetron, adapatable to various aircraft, and using manufacturer data.
With this system in place of spagetti charts, we can calculate our performance rapidly based on a lot of factors. What OPS does is allow us to use one source and combine every chart and piece of data into one calculation to come up with takeoff and landing data, as well as calculate max takeoff weights based on anticipated fuel burn, etc. It allows input of forecasts and reports, as well as inclusion of Configuration Deviation List items not applicable to a MEL...small things which of their own accord may not mean much, but which can add up to aerodynamic and performance penalties.
This includes gear extended, wet runways, close-in obstacles, etc.
What's important to understand is that OPS doesn't introduce something that wasn't there to begin with...in other words, anything we can do with OPS, we could have done with the manual charts, but in a much shorter time period, with a much higher degree of accuracy and repeatability. It even formats and prints out the data cards. It's faster than tabulated charts (tab data), whiz wheels, slide rules, etc. It's particularly helpful when a runway change, or even an ATIS change, alters the data used in the last calculation.
What I've often done in the past when I haven't had a tool like this to use, has been to carry my own book of the relevant performance charts, arranged in the proper order to allow me to rapidly make performance calculations on the fly; I've done this for each airplane I've flown, big and small.
Some airplanes provide less data than others. However, if one knows that one's performance is far in excess of that required, then minor variances in the predicted gradient are insignificant. Part 25 establishes minimum gradients. Terminal procedures establish minimum gradients and climb criteria based on obstacles, noise abatement, and air traffic control requirements. An aircraft which exceeds these minimum values by a significant number does not encroach on or compromise the minimum numbers when encountering a small degredation in climb performance.
Some manufacturers publish data with wheels down, some don't. A first segment climb ends with gear retraction, however, and where first segment data is published it is relevant.
So far as gear down operations go...it may be left down for many reasons, and a number of manufacturers do include gear down data. It may be a separate chart, or it may be a performance note showing the performance penalty to add for gear down. OPS simply makes it easier and faster to calculate.