Thanks for you answer!
Yes, Steel Beasts is a tank simulator, but I played it exactly like GT (tactical phase only) without having to scout, shoot, move etc. for yourself. It has also got an external view - you can play as a high commander, issue orders, and the AI platoons do the rest. Its very authentic (almost hyper-realistic), but the terrain mesh is too "low-res" and modern combat is harsh - fire fights are extremely short and deadly. The WW2 fights and terrain of GT are much more interesting to me. The strategic phase also makes the tactical phase more interesting: seeing the remains and ruins of former battles, dead, frozen soldiers etc.
You can look at SABOW (from Graviteam), on the GTOS engine. SABOW is a cold war game with 4 maps and 1 DLC (Iraq). The terrain is very good, the game is very realitic (and it will improve your skill/knowledge in GTOS/Mius).
I have read about the new winter DLC in GTMF - but it seems to have just large woods (with hundreds of "cloned", same looking trees) and it seems to have bad performance, even on state-of-the-art PCs (or did I get a wrong impression?) . The winter landscape of GTOS with its hills, hamlets, roads, woods and groves looks so much better to my eye. It really pushes the atmosphere and immersion of GT. And it runs perfectly on my i7-2600k@4,2GHZ with a GTX1070.
With the same amount of units, you will got less FPS in GTOS than GTMF. Furthermore, smoke perfomance was very improved some months ago, so GTMF is far better.
The performance issue is linked to the very acurate spotting system. The high number of trees in Karbusel DLC produces a drop of FPS (due to high CPU work). In GTOS, it's the same problem, since it's less optimized.
If you want a nice summer map with a diversified terrain, Shilovo is a mandatory DLC, on GTOS and GTMF.
If you want mainly snowed map, you will have to buy GTOS. On GTOS, you can buy a lot of DLC: snowed maps, cold war maps, summer maps.
If you want a better engine with updates, High definition, a lot of units, new DLC (summer maps, one snowed map now, maybe more in the future. Cold war maps will be released in the future) you can buy GTMF.
If money is not an issue, you can start with GTOS and the embeded winter maps. Then, you can try GTMF. Don't start with GTMF, otherwise you will be frustrated to not find the nice improvements from MF in GTOS.
You can try Tank Warfare, from Graviteam. In Africa. With Germans, Americans and British units. On GTMF engine.
Its a hard decision for me, which one to buy, GTOS and GTMF cost almost the same on steam. I absolutely love the setting of OS, but its hard to motivate myself learning a complicated, outdated UI, knowing that a better one is already available with MF...
Since GTMF was published, I never played GTOS again. It lacks too many improvements.