I agree with Jal here, speed bar an sprinters to get the speed into all your other horses. Back when I used to play the game to a good standard, I always done this, an I know a lot of other top trainers did. My main mistake back then was ignoring Fillies, as it was just so difficult to find any. Massive mistake, find a good filly an get it involved in everything.
Having only started looking for my ma\in group of Game Horses to breed from a few weeks ago (forget my current crop, spent a few weeks on those about 18months ago), I now have a pool of about 6 males, an 6 females for each distance, all of which seem a fair bit better than the rest (this is after about 30 seasons of quick seasons with claimers just to nab the best game horses). My plan now is to start new games an get all my Game Bred horses breeding every combo of those for each distance. Those 1st gens will only trial against each other. I am going to try and avoid trialing 1st gen horses, with 6th Gen horses an so on. I'm hoping this opening pool for each distance gives me a massive gene pool, with differing traits, so now the breeding should be straight forward. Once my 5f horses have got to a good standard I will then start incorporating their speed into the other horses, breeding them with 6f, then 1m etc. But again, I'll try to keep these breeding at the same gen level. At the start of my new breeding programme I'm going to try an avoid mixing a horse 6 gens in with a horse 2 or 3 gens in, hopefully once the offspring of that 3rd gen horse gets to the 6th gen, it can take that to a whole new level, than it would have just breeding them earlier.
One thing I have noticed since I used to play a long time ago, is that the Game form is a lot closer linked to the CK form. This wasn't always the case before. I have about 40 saved games all stocked away with game horses that won between 3 an 20 Gp1s. I will obv be using all these with my best exported horses too. Keeping the generations apart at the start likely to be my main issue, just means I have to have about 200 folders in the CK lol. I'm not sure I'm organised enough for this, but gonna give it a shot...
Although I am literally starting from scratch now, I'm hoping that the amount of time I've spent collecting saved games, an Game Breds means I will compete at a much higher level next season. Doubt I'll get too close to you guys given the head start, but hoping to cause a few shocks

I already have a 5f filly, that won everything in the game, says 7f distance but wins my 5f, 6f, an 7f trials by 4l on the bridle. And this is a lot of collected best game horses. This horse likely to be the main stay of my whole breeding programme. By far the best Game Filly I have ever came accross. Ive uploaded her this season, just to see how she goes. No expectations obviously. Ollatrim Lady it is, just making sure her running style is suited to the league races before commiting to her breeding stock

Apologies for the essay, I love these chats, fascinating to see everyone's differing styles.
Vinny