NSStringVariations.m

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        void (^benchmark)(const char *str) = ^(const char *str) {
            const long count = 10000000;
            NSDate *start = [NSDate date];
            for (long i = 0; i < count; i++) {
                (void)[[NSString alloc] initWithUTF8String:str];
            }
            NSTimeInterval t = -[start timeIntervalSinceNow];
            NSLog(@"Time to allocate @\"%s\" %ld times was %f seconds", str, count, t);
        };
        
        benchmark("hellohello"); //Tagged pointer
        benchmark("hellohelQo"); //'Q' is not in the set of characters that are packed into tagged pointer strings, since it's uncommon, and NSString saves space by using <8 bits per character for tagged strings
        benchmark("Foundation.framework"); //In the StringROM, a perfect hash table of commonly used strings built into the CoreFoundation binary
        benchmark("Foundation.framewokk"); //Not in the ROM, and too long to be tagged
    }
    return 0;
}

/*
Output on a 1.8GHz mid-2011 MacBook Air:
2015-02-18 00:29:43.699 NSStringIsWeird[9934:939189] Time to allocate @"hellohello" 10000000 times was 0.689991 seconds
2015-02-18 00:29:46.637 NSStringIsWeird[9934:939189] Time to allocate @"hellohelQo" 10000000 times was 2.936201 seconds
2015-02-18 00:29:47.839 NSStringIsWeird[9934:939189] Time to allocate @"Foundation.framework" 10000000 times was 1.202736 seconds
2015-02-18 00:29:50.671 NSStringIsWeird[9934:939189] Time to allocate @"Foundation.framewokk" 10000000 times was 2.831387 seconds
*/

For comparison, if you use -initWithString: with a constant CFString/NSString instead of doing -initWithUTF8String: with a C string, 10,000,000 allocations will take around 0.5 seconds on the machine mentioned in the comment.