Newbie Boring Bar suggestions plese

Hi Everyone, This Is my first post here. :D

I need to Bore 1.25" Al 6061t6 rod out to .75"id at 2.75"depth on my Sherline 4410. I am looking at boring bars 3/8"diameter. From what I have read I need solid carbide with an indexable insert to get that amount of hang-over and still keep stiffness. I have a home made 3/8" tool holder that clamps down using both T slots (it's three times as deep as a normal tool holder) and will be taking very shallow cuts (of course). I would like to use HSS inserts as I have found that with aluminum on this machine the sharper the insert the better and I really like the T-15 HSS that AR Warner sells.

The fact is I don't know if I need solid carbide or just Heavy metal. My research tells me that a carbide holder will do 10X overhang and M42HSS holders will do 7X. I may be wrong.

I am looking at these:
SOLID CARBIDE BORING BAR .375 MariTool

Arthur R. Warner Co. | Specialists in High Speed Steel - Kit #13 3/8 inch Boring Bar (C)

CC2900 INDEX. BORING BAR :: C Series - Carbide Boring Bars | Travers Tool

or:

CC2905 INDEX. BORING BAR :: C Series - Carbide Boring Bars | Travers Tool

Thanks in advance, I am new to all these letter codes but am learning fast.

Sincerely,
Boden

P.s. I have a background in Applied Physics so technical answers will be understood. Actually the more maths the better ;)