Opticron Imagic TGA WP 8x42 or 10x50

[Steve72]

HI all, I would some appreciate advice.  I fully intend to purchase a pair of Helios Apollo 15x70's as soon as I can find them in stock somewhere (probably June by the sounds of it). 

Until then I want to buy a pair of good quality smaller binoculars for astronomy but also general purpose/grab quickly when needed. (budget around £150).

After reading various reviews I think I have settled on Opticron Imagic (although I'm open to persuasion). My question is, which size would compliment the 15x70's the best as a second pair of bins - 8x42 or 10x50. I was thinking the versatility and wider field of view of the 8x42 would be good to have, leaving the 15x70 for more serious observation.

Also is the 10x50 a true 50mm or is it stepped down?

thanks,

Steve