Top commercial breeders use - and sell - certain crosses, such as SufTex (Suffolk x Texel), Beltex x Charollais, and frequently Texel and Dutch Texel crosses with 1/2, 1/4 and 1/8 Beltex or other Texel-type.
They'll do it a little more scientifically than you or I can manage, of course
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I've used a tup lamb I bred here, and have kept some of his progeny on. He was half Shetland and half <commercial mongrel> - his mum was a Charollais out of a Beltex x Swaley Mule.
Two of his ewe lambs out of Dutch Texel commercial shearlings are excellent and are staying on as commercial ewes. The DT cross male lambs all did well and were sold deadweight before Christmas, so finished nearly as fast and as well as any.
His progeny from my 'fleece sheep' were more varied, and at first I thought too varied. But I've got some lovely fleeces and all the males have shaped up well, given their breeding (Mums are Shetland crosses and Manxes) and would have sold well enough in the ring had I wanted to sell them that way. One went off fat late winter (his fleece wasn't special enough to warrant keeping him longer, and I wanted some hogget in the freezer before lambing) and was a very acceptable carcase for that sort of sheep.
He only gave me one ewe lamb from the primitives, and she'll not be bred from, she has an eye problem.
This year I've used a pure Shetland, just on my fleece sheep, and I am absolutely delighted with his offspring. There's not a lamb I'm not pleased with, except maybe the runt of one of the two sets of triplets. The problem he's given me is how to select who's staying when it comes to this time next year and I will want to keep
all his daughters on!
So, on limited data, my own view is that you get a more predictable - and if you chose well, excellent - outcome from a purebred tup. But since we keep our own sheep for enjoyment as much as for a lamb crop, if you fancy trying these two, well - why not? The SufTex is not an unusual choice for a terminal sire, and if you are wanting some replacement ewes, then the Texel x Lleyn could give you some interesting girls.
Do let us know how they do!