Is LINQ a real-world bottleneck (either effecting the overall or perceived performance of the application)?
Will your application be performing this operation on 1,000,000,000+ records in the real-world? If so--then you might want to consider alternatives--if not then it's like saying "we can't buy this family sedan because it doesn't drive well at 180+ MPH".
If it's "just slow" then that's not a very good reason... by that reasoning you should be writing everything in asm/C/C++, and C# should be off the table for being "too slow".
